From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2010-03-27T05:39:16+09:00
Subject: Re: changing method behavior depending on context

On Fri, Mar 26, 2010 at 5:11 PM, Marat Kamenschikov <buhiyhi@yahoo.com> wrote:
> Assume there is class A with method save which takes one param with
> default value (e.g. true). Class A instance gets save and behaves
> depending on true value.
> Assume there is class B with a field of type A. Calling save on this
> field it should behave as if save(false) was called.
> Outside of class B scope save method should behave originally.
> Something like override, but just inside of one scope.
>
> Here is some piece of code:
> class A
>  def save(validate = true)
>    validate? «INVALID»: «VALID»
>  end
> end
>
> class B
>  # something very crazy
>  def initialize
>    @a = A.new
>  end
>  def save
>    @a.save
>  end
> end
>
> A.new.save # => «INVALID»
> B.new.save # => «VALID»
> A.new.save # => «INVALID»
>
> It is meant to be used in Rails application with ActiveRecord objects,
> but it really doesn't matter much.
> The most simple way here is probably examining caller list, but is there
> a way to redef a method inside of other class' scope?

I have no clue if this works or not with ActiveRecord objects, but in
case it does, I would do this:

irb(main):006:0> class A
irb(main):007:1> def save(validate=true)
irb(main):008:2> validate ? "INVALID" : "VALID"
irb(main):009:2> end
irb(main):010:1> end
=> nil
irb(main):011:0> class B
irb(main):012:1> def initialize
irb(main):013:2> @a = A.new
irb(main):014:2> def @a.save(validate=true)
irb(main):015:3> super false
irb(main):016:3> end
irb(main):017:2> end
irb(main):018:1> def save
irb(main):019:2> @a.save
irb(main):020:2> end
irb(main):021:1> end
=> nil
irb(main):022:0> B.new.save
=> "VALID"
irb(main):023:0> A.new.save
=> "INVALID"


Although if this works for you, you could also change the save method
in class B to pass a false...

irb(main):001:0> class A
irb(main):002:1> def save(validate=true)
irb(main):003:2> validate ? "INVALID" : "VALID"
irb(main):004:2> end
irb(main):005:1> end
=> nil
irb(main):006:0> class B
irb(main):007:1> def initialize
irb(main):008:2> @a = A.new
irb(main):009:2> end
irb(main):010:1> def save
irb(main):011:2> @a.save false
irb(main):012:2> end
irb(main):013:1> end
=> nil
irb(main):014:0> A.new.save
=> "INVALID"
irb(main):015:0> B.new.save
=> "VALID"

Jesus.